Lens drive mechanism

ABSTRACT

A lens drive mechanism includes first and second members positioned adjacent to each other where the second member supports a lens group and is movable relative to the first member along an optical axis of the lens group, and a first guide shaft extending in a direction of the optical axis which is supported by the first member to be guided in the direction of the optical axis, where one end of the first guide shaft is secured to the second member. The lens drive mechanism also includes a gear rotatably supported on the first member, which does not move in the direction of the optical axis relative to the first member and has a hole at an axial center on an inner periphery of which is formed a first thread. The lens drive mechanism further includes a screw shaft on which a second thread is formed and which extends parallel to the first guide shaft where one end of the screw shaft is secured to the second member and the gear is rotatably fitted on the screw shaft with the first thread meshing with the second thread. A stopper plate is also provided which is secured to another end of each of the screw shaft and the first guide shaft, and in impact absorbing member is provided which is fitted on the first guide shaft adjacent to the stopper plate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lens drive mechanism for driving a lens group to move along an optical axis while ensuring the accurate movement of the lens group.

2. Description of the Related Art

In a conventional camera having a zoom lens (zoom compact camera), operations such as zooming, focusing, and the like, are each effected by varying a distance between two lens groups in accordance with photographing information, such as a subject distance. In such a conventional camera, the two lens groups are relatively moved, or at least one of the two lens groups is moved relative to the other, along an optical axis of the zoom lens, so as to vary the distance therebetween.

A typical drive mechanism for varying the distance between the two lens groups adopts a feed screw mechanism consisting of an externally-threaded rod (feed screw shaft) and a gear having a female screw hole engaging with the male screw. A member, e.g., a member which supports a lens group to be moved, is driven to move in the optical axis direction by the drive mechanism. A stopper is generally provided at a position corresponding to one end of the predetermined movable range of the member, so that the member may not be moved beyond the predetermined movable range. If for some reason the member moves beyond the predetermined movable range, the gear might get jammed so as to be prevented from moving along the feed screw shaft.

Recently, there has been an increasing demand for smaller zoom compact cameras, specifically lens-shutter type zoom compact cameras. In order to meet this demand it has become desirable to provide a member which functions as the aforementioned stopper, and which consumes little space in the drive mechanism of the camera.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a lens drive mechanism for driving a lens group to move along an optical axis, which is provided with a space-efficient device for preventing an occurrence of jamming in the feed screw mechanism of the drive mechanism so as to ensure the movement of the lens group.

To achieve the object mentioned above, according to an aspect of the present invention, there is provided a lens drive mechanism including first and second members positioned adjacent to each other where the second member supports a lens group and is movable relative to the first member along an optical axis of the lens group. The lens drive mechanism also includes a first guide shaft extending in a direction of the optical axis which is supported by the first member to be guided in the direction of the optical axis, where one end of the first guide shaft is secured to the second member. The mechanism further includes a gear rotatably supported on the first member so as not to move in the direction of the optical axis relative to the first member which includes a hole at an axial center on an inner periphery of which is formed a first thread, and a screw shaft on which a second thread is formed and which extends parallel to the first guide shaft, where one end of the screw shaft is secured to the second member. The gear is rotatably fitted on the screw shaft with the first thread meshing with the second thread. The lens drive mechanism also includes a stopper plate secured to another end of each of the screw shaft and the first guide shaft, and an impact absorbing member fitted on the first guide shaft adjacent to the stopper plate.

Preferably, the impact absorbing member is slidable along the first guide shaft.

Preferably, the impact absorbing member is an O-ring. The impact absorbing member may be a coil spring, a wave washer or the like which is fitted on the first guide shaft.

According to another aspect of the present invention, there is provided a zoom lens including front and rear lens groups, the zoom lens being provided with a rear lens group drive mechanism for driving the rear lens group to move along an optical axis thereof relative to the front lens group. The zoom lens includes a shutter mounting stage which supports a shutter consisting of a plurality of shutter blades, a lens supporting member which supports the rear lens group which is movable along the optical axis relative to the shutter mounting stage without rotating about the optical axis, and a guide shaft extending in a direction of the optical axis which is supported on the shutter mounting stage to be guided in the direction of the optical axis, a rear end of the guide shaft is secured to the lens supporting member. The zoom lens also comprises a gear rotatably supported on the shutter mounting stage such that the gear does not move in the direction of the optical axis relative to the shutter mounting stage, the rear also includes a hole at an axial center on an inner periphery of which is formed a first thread. The zoom lens includes a screw shaft on which a second thread is formed and which extends parallel to the guide shaft where a rear end of the screw shaft is secured to the lens supporting member. The gear is rotatably fitted on the screw shaft with the first thread meshing with the second thread. The zoom lens further includes a drive mechanism for driving the gear to rotate on the screw shaft, a stopper plate secured to another end of each of the screw shaft and the guide shaft, and an impact absorbing member fitted on the guide shaft adjacent to the stopper plate.

The present disclosure relates to subject matter contained in Japanese Patent Application No. 8-12317, filed on Jan. 26, 1996, and 8-31080, filed on Feb. 19, 1996, which are expressly incorporated herein by reference in their entireties.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below in detail with reference to the accompanying drawings in which similar elements are indicated by similar reference numerals, and wherein:

FIG. 1 is an enlarged schematic perspective view showing a part of a zoom lens barrel;

FIG. 2 is a schematic perspective view showing the part of the zoom lens barrel shown in FIG. 1 in an engaged state;

FIG. 3 is an enlarged exploded perspective view of a part of the zoom lens barrel;

FIG. 4 is a schematic perspective view illustrating a state where an AF/AE shutter unit of the zoom lens barrel is mounted to a first moving barrel;

FIG. 5 is an exploded perspective view illustrating main parts of the AF/AE shutter unit of the zoom lens barrel shown in FIGS. 1, 2, 3 and 4;

FIG. 6 is an enlarged schematic perspective view of a third moving barrel of the zoom lens barrel;

FIG. 7 is a front elevational view of a fixed lens barrel block of the zoom lens barrel;

FIG. 8 is a sectional view of an upper part of the zoom lens barrel in a maximum extended state;

FIG. 9 is a sectional view of an upper part of the zoom lens barrel, illustrating essential elements in a housed state;

FIG. 10 is a sectional view of the upper part of the zoom lens barrel shown in FIG. 9 in the maximum extended state;

FIG. 11 is a sectional view of an upper part of the zoom lens barrel in the housed state;

FIG. 12 is an exploded perspective view of the overall structure of the zoom lens barrel;

FIG. 13 is a block diagram of a controlling system for controlling an operation of the zoom lens barrel;

FIG. 14 is an exploded perspective view of a lens drive mechanism of the zoom lens barrel;

FIG. 15 is a schematic plan view of a part of the lens drive mechanism shown in FIG. 14;

FIG. 16 is a schematic sectional view of the lens drive mechanism;

FIG. 17 is a schematic sectional view of the lens drive mechanism in a state different from the state shown in FIG. 16;

FIG. 18 is an enlarged perspective view of a linear guide barrel shown in FIG. 12;

FIG. 19 is a sectional view of an upper part of a lens supporting barrel which supports a front lens group therein, and a lens fixing ring which is to be screw-engaged with the lens supporting barrel;

FIG. 20 is an enlarged perspective view of the lens supporting barrel shown in FIG. 19; and

FIG. 21 is an enlarged sectional view of a part of the lens fixing ring shown in FIG. 19.

DESCRIPTION OF TEE PREFERRED EMBODIMENT

FIG. 13 is a schematic representation of various elements which comprise a preferred embodiment of a zoom lens camera to which the present invention is applied. A concept of the present zoom lens camera will now be described with reference to FIG. 13.

The zoom lens camera is provided with a zoom lens barrel (zoom lens) 10 of a three-stage delivery type (telescoping type) having three moving barrels, namely a first moving barrel 20, a second moving barrel 19 and a third moving barrel (rotational barrel) 16, which are concentrically arranged in this order from an optical axis 0. In the zoom lens barrel 10, two lens groups are provided as a photographic optical system, namely a front lens group L1 having positive power and a rear lens group L2 having negative power.

In the camera body, a whole optical unit driving motor controller 60, a rear lens group driving motor controller 61, a zoom operating device 62, a focus operating device 63, an object distance measuring apparatus 64, a photometering apparatus 65, and an AE (i.e., automatic exposure) motor controller 66, are provided. Although the specific focusing system of the object distance measuring apparatus 64, which is used to provide information regarding the object-to-camera distance, does not form part of the present invention, one such suitable system is disclosed in commonly assigned U.S. patent application Ser. No. 08/605,759, filed on Feb. 22, 1996, the entire disclosure of which is expressly incorporated by reference herein. Although the focusing systems disclosed in U.S. patent application Ser. No. 08/605,759 are of the so-called "passive" type, other known autofocus systems (e.g., active range finding systems such as those based on infrared light and triangulation) may be used. Similarly, a photometering system as disclosed in the above-noted U.S. patent application Ser. No. 08/605,759 could be implemented as photometering apparatus 65.

The zoom operating device 62 can be provided in the form of, for example, a manually-operable zoom operating lever (not shown) provided on the camera body or a pair of zoom buttons, e.g., a "wide" zoom button and a "tele" zoom button (not shown) provided on the camera body. When the zoom operation device 62 is operated, the whole optical unit driving motor controller 60 drives a whole optical unit driving motor 25 to move the front lens group L1 and the rear lens group L2, rearwardly or forwardly without regard to a focal length and a focal point thereof. In the following explanation, forward and rearward movements of the lens groups L1 and L2 by the whole optical unit driving motor controller 60 (the motor 25) are referred to as the movement toward "tele" and the movement toward "wide" respectively, since forward and rearward movements of the lens groups L1 and L2 occur when the zoom operating device 62 is operated to "tele" and "wide" positions.

The image magnification of the visual field of a zoom finder 67 provided in the camera body varies in accordance with the variation of the focal length through the operation of the zoom operating device 62. Therefore, the photographer can perceive the variation of the focal length by observing the variation of image magnification of the visual field of the finder. In addition, the focal length, as set by the operation of the zoom operating device 62, may be a value indicated by a value on an LCD (liquid crystal display) panel (not shown) or the like.

When the focus operating device 63 is operated, the whole optical unit driving motor controller 60 drives the whole optical unit driving motor 25. At the same time, the rear lens group driving motor controller 61 drives a rear lens group driving motor 30. The driving of the whole optical unit driving motor controller 60 and the rear lens group driving motor controller 61 causes the front and rear lens groups L1 and L2 to be moved to respective positions corresponding to a set focal length and a detected object distance, thereby the zoom lens is focused on the subject.

Specifically, the focus operating device 63 is provided with a release button (not shown) provided on an upper wall of the camera body. A photometering switch and a release switch (both not shown) are synchronized with the release button. When the release button is half-depressed (half step), the focus operating device 63 turns the photometering switch ON, and the object distance measuring and photometering commands are respectively input to the object distance measuring apparatus 64 and the photometering apparatus 65.

When the release button is fully depressed (full step), the focus operating device 63 turns the release switch ON, and according to the result of the object distance measurement and a set focal length, the whole optical unit driving motor 25 and the rear lens group driving motor 30 are driven, and the focusing operation is executed, in which the front lens group L1 and the rear lens group L2 move to the focusing position. Further, an AE motor 29 of an AF/AE (i.e., autofocus/autoexposure) shutter unit (electrical unit) 21 (FIG. 11) is driven via the AE motor controller 66 to actuate a shutter 27. During the shutter action, the AE motor controller 66 drives the AE motor 29 to open shutter blades 27a of the shutter 27 for a specified period of time according to the photometering information output from the photometering apparatus 65.

When the zoom operative device 62 is operated, the zoom operating device 62 drives the whole optical unit driving motor 25 to move the front and rear lens groups L1 and L2 together as a whole in the direction of the optical axis 0 (optical axis direction). The rear lens group driving motor 30 may also be driven via the rear lens group driving motor controller 61 to move the rear lens group L2 relative to the first lens group L1. However, this may not be performed under the conventional concept of zooming in which the focal length is varied sequentially without moving the position of the focal point.

When the zoom operating device 62 is operated, the following two modes are available:

1. A mode to move the front lens group L1 and the rear lens group L2 in the optical axis direction without varying the distance therebetween by driving only the whole optical unit driving motor 25; and

2. A mode to move the front lens group L1 and the rear lens group L2 in the optical axis direction while varying the distance therebetween by driving both the whole optical unit driving motor 25 and the rear lens group driving motor 30.

In mode 1, during a zooming operation an in-focus condition cannot be obtained at all times with respect to a subject located at a specific distance. However, in a lens-shutter type camera, since the image of the subject is not observed through the photographing optical system, but through the finder optical system provided separately from the photographing optical system, it is sufficient that the subject is only focused when the shutter is released. In mode 2, during a zooming operation the front lens group L1 and the rear lens group L2 are moved without regard to whether the focal point moves, and when the shutter is released, the focusing operation (focus adjusting operation) is carried out by moving both the whole optical unit driving motor 25 and the rear lens group driving motor 30.

When the focus operating device 63 is operated in at least one part of the focal length range set by the zoom operating device 62, the whole optical unit driving motor 25 and the rear lens group driving motor 30 are driven to bring the subject into focus. The amount of movement of each lens group L1 or L2 by the whole optical unit driving motor 25 and the rear lens group driving motor 30 is determined in accordance with subject distance information provided from the object distance measuring apparatus 64, and focal length information set by the zoom operating device 62. By moving both the whole optical unit driving motor 25 and the rear lens group driving motor 30 when the focus operating device 63 is operated, the position of the lens groups L1, L2 can be flexibly controlled in comparison to lens movements controlled by cam.

The zoom lens camera of this embodiment can also be controlled in a manner such that only the magnification of the zoom finder 67 and the focal length information are varied during an operation of the zoom operating device 62, without driving either the whole optical unit driving motor 25 or the rear lens group driving motor 30. Under this type of control, when the focus operating device 63 is operated, both the whole optical unit driving motor 25 and the rear lens group driving motor 30 are moved simultaneously according to the focal length information and the subject distance information obtained by the object distance measuring apparatus 64 to move the front lens group L1 and the rear lens group L2 to respective positions determined according to the focal length and the subject distance information.

An embodiment of the zoom lens barrel according to the above concept will now be described with reference to mainly FIGS. 11 and 12.

The overall structure of the zoom lens barrel 10 will firstly be described.

The zoom lens barrel 10 is provided with the first moving barrel 20, the second moving barrel 19, the third moving barrel 16, and a fixed lens barrel block 12. The third moving barrel 16 is engaged with a cylindrical portion 12p of the fixed lens barrel block 12, and moves in the optical axis direction upon being rotated. The third moving barrel 16 is provided on an inner periphery thereof with a linear guide barrel 17, which is restricted in rotation. The linear guide barrel 17 and the third moving barrel 16 move together as a whole in the optical axis direction, with the third moving barrel 16 rotating relative to the linear guide barrel 17. The first moving barrel 20 moves in the optical axis direction with rotation thereof being restricted. The second moving barrel 19 moves in the optical axis direction, while rotating relative to the linear guide barrel 17 and the first moving barrel 20. The whole optical unit driving motor 25 is secured to the fixed lens barrel block 12. A shutter mounting stage 40 is secured to the first moving barrel 20. The AE motor 29 and the rear lens group driving motor 30 are mounted on the shutter mounting stage 40. The front lens group L1 and the rear lens group L2 are respectively supported by a lens supporting barrel (lens supporting annular member) 34 and a lens supporting barrel (second member) 50.

An O-ring 70, made of a rubber or the like, is positioned between an outer peripheral circumferential surface of the front end of the lens supporting barrel 34, and an inner peripheral circumferential surface of an inner flange portion 20b integrally formed in the front end of the first moving barrel 20 as shown in FIG. 11. The O-ring 70 prevents water from penetrating the zoom lens barrel 10 at the front end thereof between the first moving barrel 20 and the lens supporting barrel 34.

As shown in FIG. 19, the front lens group L1 consists of five lenses, namely a first lens (frontmost lens) L1a, a second lens Llb, a third lens Llc, a fourth lens Lld and a fifth lens Lle in this order from an object side to an image side, i.e., from the left hand side to the right hand side as viewed in FIG. 19.

A front positioning ring 36 for determining a distance between the second lens Llb and the third lens Llc is positioned and held between the second lens Llb and the third lens Llc. An outer peripheral surface of the positioning ring 36 is fitted on an inner peripheral surface of the lens supporting barrel 34. Likewise, a rear positioning ring 37 for determining a distance between the third lens Llc and the fourth lens Lld is positioned and held between the third lens Llc and the fourth lens Lld. An outer peripheral surface of the positioning ring 37 is fitted on an inner peripheral surface of the lens supporting barrel 34. The rear surface of the fourth lens Lld and the front surface of the fifth lens Lle are cemented to each other, so that the fourth and fifth lenses Lld, Lle are formed as a cemented or composite lens. A front circumferential edge Llf of the second lens Llb along the circumferential edge thereof contacts the rear surface of the first lens L1a. A rear circumferential edge Llg of the fifth lens Lle along the circumferential edge thereof contacts an inwardly-projecting flange 34b formed integral with the rear end of the lens supporting barrel 34.

A female thread 34a is formed on an inner periphery of a front part of the lens supporting barrel 34, as shown in FIGS. 20 or 21. A lens fixing ring 72, for fixing the first lens L1a to the lens support barrel 34, engages with the lens supporting barrel 34. With this arrangement, a male thread 72a formed on the outer peripheral surface of the lens fixing ring 72 meshes with the female thread 34a. A circular abutting surface 72b is formed on the lens fixing ring 72 on an inner peripheral surface. The circular abutting surface 72b comes into contact with a circumferential portion fp of the front surface of the first lens L1a in a state when the lens fixing ring 72 is properly screw-engaged with the lens supporting barrel 34. The circular abutting surface 72b is formed to be substantially parallel to the circumferential portion fp so that the circular abutting surface 72b and the circumferential portion fp may be brought tightly into contact with each other when the lens fixing ring 72 is properly screw-engaged with the lens supporting barrel 34.

A supporting ring portion 34c is integrally formed with the lens supporting barrel 34. The supporting ring portion 34c is located inwardly from the female thread 34a in a radial direction of the lens supporting barrel 34. The inner peripheral surface of the supporting ring portion 34c, which extends in the optical axis direction, comes into contact with an outer circumferential edge or surface op of the first lens L1a. An annular positioning surface 34d, extending substantially normal to the optical axis 0, is formed on the lens supporting barrel 34 immediately behind the supporting ring portion 34c. The circumferential edge of the rear surface of the first lens L1a comes into contact with the positioning surface 34d. With this structure, the first lens L1a is immovably held between the circular abutting surface 72b and the positioning surface 34d in the optical axis direction, and the first lens L1a is immovably held by the supporting ring portion 34c in a radial direction normal to the optical axis 0.

As shown in FIG. 21, a coating 72e is coated on the circular abutting surface 72b. The coating 72e is a waterproof coating made of a synthetic resin. In the present embodiment, Fantas Coat SF-6 (trademark of a coating produced by the Japanese Company "Origin Denki Kabushiki Kaisha") is used as the coating 72e. The front surface of the first lens L1a is formed very smooth, whereas the circular abutting surface 72b of the lens fixing ring 72 is not formed as smoothly (i.e., has a rough finish) as the front surface of the first lens L1a. This is because the first lens L1a is more minutely and accurately formed than the lens fixing ring 72 since the first lens L1a is a precision optical element. Because of the differences in the finishes, in the absence of the coating 72e on the circular abutting surface 72b, a substantial gap would be formed between the circular abutting surface 72b and the circumferential portion fp. This would be the case even if the circular abutting surface 72b was properly and tightly in contact with the circumferential portion fp by properly screw-engaging the lens fixing ring 72 with the female thread 34a. As a result, water or moisture would be able to penetrate into the lens supporting barrel 34 through the substantial gap. However, in the present embodiment, the coating 72e is applied to the circular abutting surface 72b so as to make the surface thereof a smooth surface which eliminates the substantial gap between the circular abutting surface 72b and the circumferential portion fp when the circular abutting surface 72b properly contacts the circumferential portion fp. Accordingly, the coating 72e, positioned and held between the circular abutting surface 72b and the circumferential portion fp, effectively prevents water or moisture from penetrating the lens supporting barrel 34 between the circular abutting surface 72b and the circumferential portion fp when the circular abutting surface 72b is properly and tightly in contact with the circumferential portion fp by properly screw-engaging the lens fixing ring 72 with the female thread 34a.

A circular surface 72c is formed on the lens fixing ring 72. The circular surface 72c is connected to the circular abutting surface 72b and is located immediately outward in a radial direction from the circular abutting surface 72b. A front part of the outer circumferential surface op of the first lens L1a (i.e., a circumferential edge of the first lens L1a) comes into contact with the circular surface 72c when the lens fixing ring 72 properly engages with the female thread 34a. Due to the circular surface 72c contacting the outer circumferential surface op, the watertight structure between the circular abutting surface 72b and the circumferential portion fp, that is realized by the coating 72e, is enhanced. That is, a highly efficient watertight connection between the first lens L1a and the lens fixing ring 72 is realized by providing both the coating 72e and the circular surface 72c with the lens fixing ring 72.

An annular recessed portion 34e is formed on the lens supporting barrel 34 between the female thread 34a and the supporting ring portion 34c. As shown in FIG. 11, in a state where the lens fixing ring 72 is properly screw-engaged with the female thread 34a, a rear end 72d of the lens fixing ring 72 is positioned in the annular recessed portion 34e with the rear end 72d not contacting the bottom (i.e., rearmost end) of the recessed portion 34e. In particular, an annular space is formed in the annular recessed portion 34e between the rear end 72d and the bottom of the recessed portion 34e.

The fixed lens barrel block 12 is fixed in front of an aperture plate 14 fixed to the camera body. The aperture plate 14 is provided on a center thereof with a rectangular-shaped aperture 14a which forms the limits of each frame exposed. The fixed lens barrel block 12 is provided on an inner periphery of the cylindrical portion 12p, with a female helicoid 12a, and also a plurality of linear guide grooves 12b each extending parallel to the optical axis 0, i.e., extending in the optical axis direction. At the bottom of one of the linear guide grooves 12b, namely 12b', a code plate 13a, having a predetermined code pattern, is fixed. The code plate 13a extends in the optical axis direction and extends along substantially the whole of the length of the fixed lens barrel block 12. The code plate 13a is part of a flexible printed circuit board 13 positioned outside the fixed lens barrel block 12.

As shown in FIGS. 7 and 12, in the fixed lens barrel block 12, a gear housing 12c is provided which is recessed outwardly from an inner periphery of the cylindrical portion 12p of the fixed lens barrel block 12 in a radial direction while extending in the optical axis direction. In the gear housing 12c, a driving pinion 15 is rotatably held and extends in the optical axis direction. Both ends of an axial shaft 7 of the driving pinion 15 are rotatively supported by a supporting hollow 4, provided in the fixed lens barrel block 12, and a supporting hollow 31a, provided on a gear supporting plate 31 fixed on the fixed lens barrel block 12 by set screws (not shown), respectively. Part of the teeth of the driving pinion 15 project inwardly from the inner periphery of the cylindrical portion 12p of the fixed lens barrel block 12 so that the driving pinion 15 meshes with an outer peripheral gear 16b of the third moving barrel 16, as shown in FIG. 7.

On an inner periphery of the third moving barrel 16, a plurality of linear guide grooves 16c are formed, each extending parallel to the optical axis 0. At an outer periphery of the rear end of the third moving barrel 16, a male helicoid 16a and the aforementioned outer peripheral gear 16b are provided as shown in FIG. 6. The male hellcold 16a engages with the female helicoid 12a of the fixed lens barrel block 12. The outer peripheral gear 16b engages with the driving pinion 15. The driving pinion 15 has an axial length sufficient to be capable of engaging with the outer peripheral gear 16b throughout the entire range of movement of the third moving barrel 16 in the optical axis direction.

As shown in FIGS. 12 and 18, the linear guide barrel 17 is provided, on a rear part of an outer periphery thereof, with a rear end flange 17d. The rear end flange 17d has a plurality of engaging projections 17c each projecting away from the optical axis 0 in a radial direction. The linear guide barrel 17 is further provided with a retaining flange 17e in front of the rear end flange 17d. A circumferential groove 17g is formed between the rear end flange 17d and the retaining flange 17e. The retaining flange 17e has a radius smaller than the rear end flange 17d. The retaining flange 17e is provided with a plurality of cutout portions 17f. Each of the cutout portions 17f allows a corresponding engaging projection 16d to be inserted into the circumferential groove 17g, as shown in FIG. 11.

The third moving barrel 16 is provided, on an inner periphery of the rear end thereof, with a plurality of engaging projections 16d. Each of the engaging projections 16d projects towards the optical axis 0 in a radial direction. By inserting the engaging projections 16d into the circumferential groove 17g, through the corresponding cutout portions 17f, the engaging projections 16d are positioned in the circumferential groove 17g between the flanges 17d and 17e (see FIG. 11). By rotating the third moving barrel 16 relative to the linear guide barrel 17, the engaging projections 16d are engaged with the linear guide barrel 17.

An aperture plate 23 having a rectangular-shaped aperture 23a approximately the same shape as the aperture 14a is fixed to the read-end of the linear guide barrel 17.

The relative rotation of the linear guide barrel 17, with respect to the fixed lens barrel block 12, is restricted by the slidable engagement of the plurality of engaging projections 17c with the corresponding linear guide grooves 12b, formed parallel to the optical axis 0.

A contacting terminal 9 is fixed to one of the engaging projections 17c, namely 17c'. The contacting terminal 9 is in slidable contact with the code plate 13a, fixed to the bottom of the linear guide groove 12b' to generate signals corresponding to focal length information during zooming.

A plurality of linear guide grooves 17a are formed on the inner periphery of the linear guide barrel 17, each extending parallel to the optical axis 0. A plurality of lead slots (cam slots) 17b are also formed on the linear guide barrel 17 as shown in FIGS. 12 or 18. The lead slots 17b are each formed oblique (inclined) to the optical axis 0.

The second moving barrel 19 engages with the inner periphery of the linear guide barrel 17. On the inner periphery of the second moving barrel 19, a plurality of lead grooves 19c are provided in a direction inclined oppositely to the lead slots 17b. Each lead groove 19c is oblique to both the optical axis direction and a circumferential direction of the linear guide barrel 17 by a predetermined angle, similar to each lead slot 17b. On the outer periphery of the rear end of the second moving barrel 19, a plurality of follower projections 19a are provided. Each of the follower projections 19a has a trapezoidal cross-sectional shape projecting away from the optical axis 0 in a radial direction. Follower pins 18 are positioned in the follower projections 19a. Each follower pin 18 consists of a ring member 18a, and a center fixing screw 18b which supports the ring member 18a on the corresponding follower projection 19a. The follower projections 19a are in slidable engagement with the lead slots 17b of the linear guide barrel 17, and the follower pins 18 are in slidable engagement with the linear guide grooves 16c of the third moving barrel 16. With such an arrangement, when the third moving barrel 16 rotates, the second moving barrel 19 moves linearly in the optical axis direction, while rotating.

On the inner periphery of the second moving barrel 19, the first moving barrel 20 is engaged. The first moving barrel 20 is provided on an outer periphery of the rear thereof with a plurality of follower pins 24 each engaging with the corresponding inner lead groove 19c. At the same time the first moving barrel 20 is guided linearly by a linear guide member 22. The first moving barrel 20 is provided at the front end thereof with a decorative plate 41.

As shown in FIGS. 1 and 2, the linear guide member 22 is provided with an annular member 22a, a pair of guide legs 22b and a plurality of engaging projections 28. The pair of guide legs 22b project from the annular member 22a in the optical axis direction. The plurality of engaging projections 28 each project from the annular member 22a away from the optical axis 0 in a radial direction. The engaging projections 28 slidably engage with the linear guide grooves 17a. The guide legs 22b are respectively inserted into linear guides 40c between the inner peripheral surface of the first moving barrel 20 and the AF/AE shutter unit 21.

The annular member 22a of the linear guide member 22 is connected to the rear of the second moving barrel 19, such that the linear guide member 22 and the second moving barrel 19 are capable of moving along the optical axis 0 as a whole and relatively rotating around the optical axis 0. The linear guide member 22 is further provided on the outer periphery of the rear end thereof with a rear end flange 22d. The linear guide member 22 is further provided in front of the rear end flange 22d with a retaining flange 22c. A circumferential groove 22f is formed between the rear end flange 22d and the retaining flange 22c. The retaining flange 22c has a smaller radius than the rear end flange 22d. The retaining flange 22c is provided with a plurality of cutout portions 22e, as shown in FIGS. 7 or 8, each allowing a corresponding engaging projection 19b to be inserted into the circumferential groove 22f, as shown in FIG. 11.

The second moving barrel 19 is provided on an inner periphery of the rear end thereof with a plurality of engaging projections 19b, each projecting towards the optical axis 0 in a radial direction. By inserting the engaging projections 19b into the circumferential groove 22f through the corresponding cutout portions 22e, the engaging projections 19b are positioned in the circumferential groove 22f between the flanges 22c and 22d. By rotating the second moving barrel 19 relative to the linear guide member 22, the engaging projections 19b are engaged with the linear guide member 22. With the above structure, when the second moving barrel 19 rotates in the forward or reverse rotational direction, the first moving barrel 20 moves linearly forwardly or rearwardly along the optical axis 0, but is restricted from rotating.

At the front of the first moving barrel 20, a barrier apparatus 35 having barrier blades 48a and 48b is mounted. On an inner peripheral face of the first moving barrel 20, the AF/AE shutter unit 21 having the shutter 27, consisting of three shutter blades 27a, is engaged and fixed as shown in FIG. 15. The AF/AE shutter unit 21 is provided with a plurality of fixing holes 40a formed at even angular intervals on the outer periphery of the shutter mounting stage 40. Only one of the fixing holes 40a appears in each of FIGS. 1-5.

The aforementioned plurality of follower pins 24, which engage with the inner lead grooves 19c, also serve as a device for fixing the AF/AE shutter unit 21 to the first moving barrel 20. The follower pins 24 are inserted in holes 20a, formed on the first moving barrel 20, and fixed in the fixing holes 40a. With this arrangement the AF/AE shutter unit 21 is secured to the first moving barrel 20 as shown in FIG. 4. In FIG. 4 the first moving barrel 20 is indicated by phantom lines. The follower pins 24 may be fixed by an adhesive, or the pins 24 may be formed as screws to be screwed into the fixing holes 40a.

As illustrated in FIGS. 5 and 12, the AF/AE shutter unit 21 is provided with the shutter mounting state 40, a shutter blade supporting ring 46 fixed on the rear of the shutter mounting stage 40 so as to be located inside the shutter mounting stage 40, and the lens supporting barrel 50 supported in a state of being capable of movement relative to the shutter mounting stage 40. The shutter mounting stage 40 supports the lens supporting barrel 34, the AE motor 29, and the rear lens group driving motor 30. The shutter mounting stage 40 is provided with an annular member 40f having a circular aperture 40d. The shutter mounting stage 40 is also provided with three legs 40b which project rearward from the annular member 40f. Three slits are defined between the three legs 40b. Two of the slits comprise the aforementioned linear guides 40c, which slidably engage with the respective pair of guide legs 22b of the linear guide member 22 so as to guide the movement of the linear guide member 22.

The shutter mounting stage 40 supports an AE gear train 45 which transmits a rotation of the AE motor 29 to the shutter 27, a lens driving gear train 42 which transmits rotation of the rear lens group driving motor 30 to a screw shaft 43, photointerrupters 56 and 57 which are connected to a flexible printed circuit board 6, and rotating disks 58 and 59 which have a plurality of radially formed slits provided in the circumferential direction. An encoder for detecting whether the rear lens group driving motor 30 is rotating and for detecting an amount of rotation of the rear lens group driving motor 30 consists of the photointerrupter 57 and the rotating disk 59. An AE motor encoder for detecting whether the AE motor 29 is rotating and for detecting an amount of rotation of the AE motor 29 consists of the photointerrupter 56 and the rotating disk 58.

The shutter 27, a supporting member 47 which pivotally supports the three shutter blades 27a of the shutter 27, and a circular driving member 49, which gives rotative power to the shutter blades 27a, are positioned between the shutter mounting stage 40 and the shutter blade supporting ring 46, secured to the shutter mounting stage 40. The circular driving member 49 is provided with three operating projections 49a at even angular intervals, which respectively engage with each of the three shutter blades 27a. As shown in FIG. 11, the front end of the shutter blade supporting ring 46 is provided with a circular aperture 46a and with three supporting holes 46b positioned at even angular intervals around the circular aperture 46a. Two deflection restricting surfaces 46c are formed on the outer periphery of the shutter blade supporting ring 46. Each deflection restricting surface 46c is exposed outwardly from the corresponding linear guide 40c and slidably supports the inner peripheral face of the corresponding guide leg 22b.

The supporting member 47, positioned in front of the shutter blade supporting ring 46, is provided with a circular aperture 47a, aligned with the circular aperture 46a of the shutter blade supporting ring 46, and with three pivotal shafts 47b (only one of which is illustrated in FIG. 5) at respective positions opposite the three supporting holes 46b. Each shutter blade 27a is provided at one end thereof with a hole 27b into which the corresponding pivotal shaft 47b is inserted, so that each shutter blade 27a is rotatable about the corresponding pivotal shaft 47b. The major part of each shutter blade 27a that extends normal to the optical axis 0 from the pivoted end, is formed as a light interceptive portion. All three light interceptive portions of the shutter blades 27a together prevent ambient light, which enters the front lens group L1, from entering the circular apertures 46a and 47a when the shutter blades 27a are closed. Each shutter blade 27a is further provided between the hole 27b and the light interceptive portion, with a slot 27c, through which the corresponding operating projection 49a is inserted. The supporting member 47 is fixed to the shutter blade supporting ring 46 in such a manner that each shaft 47b, which supports the corresponding shutter blade 27a, is engaged with the corresponding supporting hole 46b of the shutter blade supporting ring 46.

A gear portion 49b is formed on a part of the outer periphery of the circular driving member 49. The gear portion 49b meshes with one of the plurality of gears in the gear train 45 to receive the rotation from the gear train 45. The supporting member 47 is provided, at respective positions close to the three pivotal shafts 47b, with three arc grooves 47c each arched along a circumferential direction. The three operating projections 49a of the circular driving ring 49 engage with the slots 27c of the respective shutter blades 27a through the respective arc grooves 47c. The shutter blade supporting ring 46 is inserted from the rear of the shutter mounting stage 40, to support the circular driving ring 49, the supporting member 47 and the shutter 27, and is fixed on the shutter mounting stage 40 by set screws 90 respectively inserted through holes 46x provided on the shutter blade supporting ring 46.

Behind the shutter blade supporting ring 46, the lens supporting barrel 50, supported to be able to move relative to the shutter mounting stage 40 via guide shafts 51 and 52, is positioned. The shutter mounting stage 40 and the lens supporting barrel 50 are biased in opposite directions away from each other by a coil spring (biasing compression spring) 3 fitted on the guide shaft 51, and therefore play between the shutter mounting stage 40 and the lens supporting barrel 50 is reduced. In addition, a driving gear 42a, provided as one of the gears in the gear train 42, is provided with a female thread hole (not shown) at the axial center thereof and is restricted to move in the axial direction. The screw shaft 43, one end of which is fixed to the lens supporting barrel 50, engages with the female thread hole. Accordingly, the driving gear 42a and the screw shaft 43 together constitute a feed screw mechanism. In such a manner, when the driving gear 42a rotates forwardly or reversely due to driving by the rear lens group driving motor 30, the screw shaft 43 respectively moves forwardly or rearwardly with respect to the driving gear 42a, and therefore the lens supporting barrel 50, which supports the rear lens group L2, moves relative to the front lens group L1.

A holding member 53 is fixed at the front of the shutter mounting stage 40. The holding member 53 holds the motors 29 and 30 between the holding member 53 and the shutter mounting stage 40. The holding member 53 has a metal holding plate 55 fixed at the front of the holding member 53 by set screws 99. The motors 29, 30 and the photointerrupers 56, 57 are connected to the flexible printed circuit board 6. One end of the flexible printed circuit board 6 is fixed to the shutter mounting stage 40.

After the first, second and third moving barrels 20, 19 and 16, and the AF/AE shutter unit 21, etc. are assembled, the aperture plate 23 is fixed to the rear of the linear guide barrel 17, and an annular retaining member 33 is fixed at the front of the fixed lens barrel block 12.

A device for preventing jamming in a feed screw mechanism used for moving the rear lens group L2 along the optical axis 0 relative to the front lens group L1 will be hereinafter discussed.

In addition to being provided with the above-mentioned drive mechanism for moving the rear lens group L2 with respect to the front lens group L1 along the optical axis 0, the AF/AE shutter unit 21 is also provided with a device which detects whether the rear lens group L2 reaches a predetermined initial position relative to the front lens group L1. In a focusing operation, the rear lens group L2 is driven to move rearwardly from an initial position away from the front lens group L1 along the optical axis 0 by an amount necessary for focusing. Subsequently, the rear lens group L2 is driven to move back to the initial position after a shutter release operation has been completed. The rear lens group L2 is controlled so as to be located at the initial position, immediately after the main switch of the camera is turned ON, immediately after a shutter release operation has been completed, and when the main switch of the camera is in an OFF state.

The device for detecting whether the rear lens group L2 reaches the initial position will be discussed with reference to FIGS. 14-17.

The lens supporting barrel 50 is guided along the optical axis 0 by the guide shafts 51, 52. Rear ends of the guide shafts 51, 52 are respectively fixed in bosses 50b, 50c which are integrally formed on the lens supporting barrel 50. The guide shaft 51 is slidably inserted into a bearing 51a fixed on the shutter mounting stage 40, so as to be guided in the optical axis direction. A front end of the guide shaft 52 is free, and the guide shaft 52 slidably fits in a supporting groove 40i (see FIG. 5) which is formed on the shutter mounting stage 40 and recessed inwardly in a radial direction of the shutter mounting stage 40.

Due to such a structure in which the guide shaft 52 is positioned in the supporting groove 40i, when the lens supporting barrel 50 moves along the optical axis 0 with respect to the shutter mounting stage 40, the lens supporting barrel 50 is prevented from rotating about the screw shaft 43 with respect to the shutter mounting stage 40. In other words, but for the guide shaft 52, the lens supporting barrel 50 would rotate about the screw shaft 43 with respect to the shutter mounting stage 40 when the screw shaft 43 is driven to move in the optical axis direction by rotation of the driving gear 42a, even though the guide shaft 51 is provided parallel to the screw shaft 43. This is because the screw shaft 43 and the guide shaft 51 are closely arranged in parallel to each other.

The rear end of the screw shaft 43 is secured to a boss 50a formed on the shutter mounting stage 40 proximate to the boss 50b. The driving gear 42a, having the female screw hole (not shown) at the axial center as noted above, is rotatably fitted on the screw shaft 43, with the female screw hole engaging with a male screw formed on the screw shaft 43. The rearward movement of the driving gear 42a along the screw shaft 43 is restricted by the shutter mounting stage 40. While the forward movement of the driving gear 42a along the screw shaft 43 is restricted by a supporting ring 53a integrally formed on the holding member 53, as illustrated in FIG. 14. Due to this structure, the driving gear 42a is prevented from moving along the screw shaft 43 relative to the shutter mounting stage 40. In other words, the distance between the driving gear 42a and the shutter mounting stage 40 is constant.

When the driving gear 42a is driven to rotate by the rear lens group driving motor 30, the screw shaft 43 moves along the axis, i.e., along the optical axis direction, relative to the driving gear 42a, which causes the rear lens group L2 which is supported by the lens supporting barrel 50, to move forwardly or rearwardly along the optical axis 0 relative to the front lens group L1. In order to prevent the occurrence of backlash between the screw shaft 43 and the driving gear 42a, the coil spring 3 is fitted on the guide shaft 51 between the bearing 51a and the boss 50b, as shown in FIG. 15. Due to the coil spring 3, the lens supporting barrel 50 is always biased rearwardly away from the shutter mounting stage 40 along the optical axis 0. This prevents backlash from occurring between the screw shaft 43 and the driving gear 42a.

A photointerrupter 301 and a light interrupting member 302 are provided adjacent to each other at a front end of the shutter mounting stage 40 in the vicinity of the metal holding plate 55. The photointerrupter 301 and the light interrupting member 302 together constitute a detector for detecting whether the rear lens group L2 reaches the aforementioned initial position relative to the front lens group L1. The photointerrupter 301 is mounted on a part of the flexible circuit board 6 and fixed on the shutter mounting stage 40. The light interrupting member 302 has a cylindrical body, at rear and front ends of which a light intercepting plate 302a and an engaging projection 302b are integrally formed, respectively.

The light interrupting member 302 is slidably fitted on a shaft 303. The front and rear ends of the shaft 303 are supported by the metal holding plate 55 and the holding member 53, respectively, as shown in FIGS. 16 or 17. A coil spring (biasing compression spring) 304 is disposed on the shaft 303 to be held between the metal holding plate 55 and the front end of the light interrupting member 302, so that the light interrupting member 302 is always biased rearwardly toward the shutter mounting stage 40 in the optical axis direction.

A slit 301a extending in the optical axis direction is formed on the photointerrupter 301 as shown in FIG. 14. The light intercepting plate 302a is capable of moving in the slit 301a to interrupt a light path OP formed approximately in the middle of the slit 301a. Namely, a front part of the light intercepting plate 302a is positioned inside the slit 301a but outside the light path OP when the light interrupting member 302 is located at a retracted position (the position shown in FIG. 17) due to the biasing force of the coil spring 304. While the front part of the light intercepting plate 302a is positioned inside the slit 301a to interrupt the light path OP when the light interrupting member 302 moves forwardly to a predetermined position, against the biasing force of the coil spring 304, as shown in FIGS. 15 or 16.

A stopper plate 306 is secured to the front end of each of the screw shaft 43 and the guide shaft 51 through a washer 305. An engaging pin 306a is integrally formed on the stopper plate 306. The engaging pin 306a is capable of engaging with the engaging projection 302b of the light interrupting member 302. Namely, when the lens supporting barrel 50, which supports the rear lens group L2, moves forwardly to predetermined position close to a front extremity of the movable range of the lens supporting barrel 50 relative to the shutter mounting stage 40, the engaging pin 306a engages with the engaging projection 302b. Thereafter, when the lens supporting barrel 50 moves further forward, the engaging pin 306a further advances to move the engaging projection 302b forwardly against the biasing force of the coil spring 304. Thereafter, when the rear lens group L2 reaches the initial position relative to the front lens group L1, i.e., when the lens supporting barrel 50 reaches an initial position relative to the shutter mounting stage 40, the light intercepting plate 302a intercepts the light path OP.

By monitoring the output of the photointerrupter 301, it can be detected whether the rear lens group L2 reaches the initial position, i.e., whether the lens supporting barrel 50 reaches the initial position, by a CPU (not shown) provided in the camera for controlling various operations (focusing operation, photometering operation, etc.). When the CPU detects that the rear lens group L2 reaches the initial position, the CPU controls the rear lens group driving motor 30 to stop so as not to further move the rear lens group L2 forwardly relative to the front lens group L1. Due to this structure, when the rear lens group L2 moves toward the front lens group L1, the rear lens group L2 does not move beyond the initial position, but surely stops at the initial position, which also prevents an occurrence of jamming of the driving gear 42a. Even if the lens supporting barrel 50 should be driven beyond the front extremity of the movable range of the lens supporting barrel 50 relative to the shutter mounting stage 40 by the rear lens group driving motor 30, such an occurrence of jamming of the driving gear 42a is also prevented since the coil spring 3 functions as a bumper to alleviate an impact which might occur between the shutter mounting stage 40 and the lens supporting barrel 50.

An O-ring (impact absorbing member) 307 made of an elastic member such as rubber is fitted on the guide shaft 51 between the stopper plate 306 and the bearing 51a. Additionally, the O-ring 307 may be formed from other types of elastic materials. The O-ring 307 normally remains at a frontmost position on the guide shaft 51 immediately behind the stopper plate 306 as shown in FIG. 15, but is slidable along the guide shaft 51. The O-ring 307 serves as a bumper to alleviate an impact occurring between the stopper plate 306 and a front end 51b of the bearing 51a, and between the stopper plate 306 and the stopper ring 53a, if the lens supporting barrel 50 should be accidentally driven to move backwardly beyond a rear extremity of the movable range of the lens supporting barrel 50 relative to the shutter mounting stage 40 by the rear lens group driving motor 30.

In order to ensure the impact-alleviating effect of the O-ring 307, a front face of the supporting ring 53a and the front end 51b of the bearing 51a are disposed to lie substantially in a common plane perpendicular to the optical axis 0, i.e., perpendicular to either the screw shaft 43 or the guide shaft 51. Due to this structure, the supporting ring 53a never bumps against the stopper plate 306, rather the front end 51b of the bearing 51a bumps against the O-ring 307 in the case where the lens supporting barrel 50 accidentally overruns backwardly beyond the rear extremity of the movable range of the lens supporting barrel 50 relative to the shutter mounting stage 40. Further, this structure alleviates an impact occurring between the stopper plate 306 and the front end 51b of the bearing 51a, and between the stopper plate 306 and the stopper ring 53a, which prevents the driving gear 42a from jamming and ensures a proper engagement of the driving gear 42a with the screw shaft 43.

Although the front face of the supporting ring 53a and the front end 51b of the bearing 51a in the present embodiment are disposed in substantially in a common plane perpendicular to the optical axis 0, it is not necessary for the front face of the supporting ring 53a and the front end 51b of the bearing 51a to be disposed as such, as long as the front end 51b can bump against the O-ring 307 without the supporting ring 53a bumping against the stopper plate 306.

In addition, the O-ring 307 may be replaced by a coil spring, a wave washer or the like which is fitted on the guide shaft 51.

In the above-described embodiment of the zoom lens barrel 10, although the zoom lens optical system consists of two movable lens groups, namely the front lens group L1 and the rear lens group L2, it should be understood that the present invention is not limited to the present embodiment disclosed above, but the present invention may also be applied to another type of zoom lens optical system including one or more fixed lens groups.

In addition, in the above embodiment, the rear lens group L1 is provided as a component of the AF/AE shutter unit 21, and the AE motor 29 and the rear lens group driving motor 30 are mounted to the AF/AE shutter unit 21. With such a structure, the structure for supporting the front and rear lens groups L1 and L2 and the structure for driving the rear lens group L2 are both simplified. Instead of adopting such a structure, the zoom lens barrel 10 may also be realized in such a manner by making the rear lens group L2 a member separate from the AF/AE shutter unit 21, which is provided with the shutter mounting stage 40, the circular driving member 49, the supporting member 47, the shutter blades 27, the shutter blade supporting ring 46 and the like, and that the rear lens group L2 is supported by a supporting member other than the AF/AE shutter unit 21.

In the zoom lens camera of the present embodiment, the operation by rotation of the whole optical unit driving motor 25 and the rear lens group driving motor 30 will now be described with reference to FIGS. 8-11.

As shown in FIGS. 9 or 11, when the zoom lens barrel 10 is at the most retracted (withdrawn) position, i.e., the lens-housed condition, when the power switch is turned ON, the whole optical unit driving motor 25 is driven to rotate its drive shaft in the forward rotational direction by a small amount. This rotation of the motor 25 is transmitted to the driving pinion 15 through a gear train 26, which is supported by a supporting member 32 integrally formed with the fixed lens barrel block 12, to rotate the third moving barrel 16 in one predetermined rotational direction to advance forwardly along the optical axis 0. Therefore, the second moving barrel 19 and the first moving barrel 20 are each advanced by a small amount in the optical axis direction, along with the third moving barrel 16. Consequently, the camera is in a state capable of photographing, with the zoom lens positioned at the widest position, i.e., the wide end. At this stage, due to the fact that the amount of movement of the linear guide barrel 17 with respect to the fixed lens barrel block 12 is detected through the relative slide between the code plate 13a and the contacting terminal 9, the focal length of the zoom lens barrel 10, i.e., the front and rear lens groups L1 and L2, is detected.

In the photographable state as above described, when the aforementioned zoom operating lever is manually moved towards a "tele" side, or the "tele" zoom button is manually depressed to be turned ON, the whole optical unit driving motor 25 is driven to rotate its drive shaft in the forward rotational direction through the whole optical unit driving motor controller 60 so that the third moving barrel 16 rotates in the rotational direction to advance along the optical axis 0 via the driving pinion 15 and the outer peripheral gear 16b. Therefore, the third moving barrel 16 is advanced from the fixed lens barrel block 12 according to the relationship between the female hellcold 12a and the male helicoid 16a. The linear guide barrel 17 moves forwardly in the optical axis direction together with the third moving barrel 16, without relative rotation to the fixed lens barrel block 12, according to the relationship between the engaging projections 17c and the linear guide grooves 12b. At this time, the simultaneous engagement of the follower pins 18 with the respective lead slots 17b and linear guide grooves 16c causes the second moving barrel 19 to move forwardly relative to the third moving barrel 16 in the optical axis direction, while rotating together with the third moving barrel 16 in the same rotational direction relative to the fixed lens barrel block 12. The first moving barrel 20 moves forwardly from the second moving barrel 19 in the optical axis direction, together with the AF/AE shutter unit 21, without relative rotation to the fixed lens barrel block 12, due to the above-noted structures in which the first moving barrel 20 is guided linearly by the linear guide member 22 and in which the follower pins 24 are guided by the lead grooves 19c. During such movements, according to the fact that the moving position of the linear guide barrel 17 with respect to the fixed lens barrel block 12 is detected through the relative slide between the code plate 13a and the contacting terminal 9, the focal length set by the zoom operation device 62 is detected.

Conversely, when the zoom operating lever is manually moved towards a "wide" side, or the "wide" zoom button is manually depressed to be turned ON, the whole optical unit driving motor 25 is driven to rotate its drive shaft in the reverse rotational direction through the whole optical unit driving motor controller 60 so that the third moving barrel 16 rotates in the rotational direction to retract into the fixed lens barrel block 12 together with the linear guide barrel 17. At the same time, the second moving barrel 19 is retracted into the third moving barrel 16, while rotating in the same direction as that of the third moving barrel 16, and the first moving barrel 20 is retracted into the rotating second moving barrel 19 together with the AF/AE shutter unit 21. During the above retraction driving, as in the case of advancing driving as above described, the rear lens group driving motor 30 is not driven.

While the zoom lens barrel 10 is driven during the zooming operation, since the rear lens group driving motor 30 is not driven, the front lens group L1 and the rear lens group L2 move as a whole, maintaining a constant distance between each other, as shown in FIGS. 8 or 10. The focal length input via the zoom code plate 13a and the contacting terminal 9 is indicated on an LCD panel (not shown) provided on the camera body.

At any focal length set by the zoom operating device 62, when the release button is depressed by a half-step, the object distance measuring apparatus 64 is actuated to measure a current subject distance. At the same time the photometering apparatus 65 is actuated to measure a current subject brightness. Thereafter, when the release button is fully depressed, the whole optical unit driving motor 25 and the rear lens group driving motor 30 are each driven by respective amounts dictated according to the focal length information set in advance and the subject distance information obtained from the object distance measuring apparatus 64 so that the front and rear lens groups L1 and L2 are respectively moved to specified positions to obtain a specified focal length to bring the subject into focus. Immediately after the subject is brought into focus, the AE motor 29 is driven via the AE motor controller 66 to rotate the circular driving member 49 by an amount corresponding to the subject brightness information obtained from the photometering apparatus 65 so that the shutter 27 is driven to open the shutter blades 27a by a specified amount which satisfies the required exposure. Immediately after such a shutter release operation, in which the three shutter blades 27a are opened and subsequently closed, is completed, the whole optical unit driving motor 25 and the rear lens group driving motor 30 are both driven to move the front lens group L1 and the rear lens group L2 to the respective initial positions which they were at prior to a shutter release.

In the present embodiment of the zoom lens barrel 10, "Fantas Coat SF-6" is used as the coating 72e. However, a different type of coating may be used as the coating 72e as long as it is waterproof and makes the circular abutting surface 72b a smooth surface to form substantially no gap between the circular abutting surface 72b and the circumferential portion fp.

Obvious changes may be made in the specific embodiments of the present invention described herein, such modifications being within the spirit and scope of the invention claimed. It is indicated that all matter contained herein is illustrative and does not limit the scope of the present invention. 

What is claimed is:
 1. A lens drive mechanism comprising:first and second members positioned adjacent to each other, said second member supporting a lens group, said second member being movable relative to said first member along an optical axis of said lens group; a first guide shaft extending in a direction of said optical axis, said first guide shaft being supported by said first member to be guided in said direction of said optical axis, one end of said first guide shaft being secured to said second member; a gear rotatably supported on said first member so as not to move in said direction of said optical axis relative to said first member, said gear defining a hole at an axial center, and a first thread formed on an inner periphery of said hole; a screw shaft on which a second thread is formed which extends parallel to said first guide shaft, one end of said screw shaft being secured to said second member, said gear being rotatably fitted to said screw shaft with said first thread meshing with said second thread; a stopper plate secured to another end of each of said screw shaft and said first guide shaft; and an impact absorbing member fitted on said first guide shaft adjacent to said stopper plate.
 2. The lens drive mechanism according to claim 1, wherein said impact absorbing member is slidable along said first guide shaft.
 3. The lens drive mechanism according to claim 1, wherein said impact absorbing member is an O-ring.
 4. The lens drive mechanism according to claim 1, wherein said first member supports a shutter having a plurality of shutter blades.
 5. The lens drive mechanism according to claim 4, wherein said first member supports a motor for driving said shutter.
 6. The lens drive mechanism according to claim 1, further comprising a drive mechanism for driving said gear to rotate about said screw shaft.
 7. The lens drive mechanism according to claim 6, wherein said drive mechanism comprises a motor for driving said gear to rotate about said screw shaft, said motor being supported by said first member.
 8. The lens drive mechanism according to claim 1, further comprising a bearing fixed on said first member, said bearing supporting and guiding said first guide shaft in said direction of said optical axis.
 9. The lens drive mechanism according to claim 1, further comprising a supporting member which supports said gear so that said gear does not move in said direction of said optical axis relative to said first member, wherein said impact absorbing member is fitted on said first guide shaft so as to allow said bearing to contact said impact absorbing member while preventing said supporting member from contacting said stopper plate.
 10. The lens drive mechanism according to claim 1, wherein said impact absorbing member is an elastic member.
 11. The lens drive mechanism according to claim 1, wherein a length of said first guide shaft is substantially equal to a length of said screw shaft.
 12. The lens drive mechanism according to claim 1, further comprising a coil spring fitted on said first guide shaft between said bearing and said second member so as to bias said second member in a direction along said optical axis away from said first member.
 13. The lens drive mechanism according to claim 1, further comprising a detector which detects whether said second member reaches an initial position relative to said first member along said optical axis, said detector being provided on said first member.
 14. The lens drive mechanism according to claim 13, wherein said detector comprises a photointerrupter fixed on said first member and a light interrupting member slidably supported on said first member for movement in said direction of said optical axis.
 15. The lens drive mechanism according to claim 14, wherein said stopper plate comprises an integrally formed engaging pin, and wherein said engaging pin comes into contact with said light interrupting member and moves said light interrupting member in said direction of said optical axis so that said light interrupting member interferes with a light path of said photointerrupter when said second member is driven to move to said initial position of said second member relative to said first member.
 16. The lens drive mechanism according to claim 1, further comprising a second guide shaft extending parallel to said first guide shaft, said second guide shaft being supported on said first member to be guided in said direction of said optical axis, one end of said second guide shaft being secured to said second member, wherein said first and second guide shafts are positioned substantially opposite to each other relative to said optical axis.
 17. The lens drive mechanism according to claim 1, wherein said first guide shaft and said screw shaft are positioned adjacent to each other.
 18. A zoom lens including a front lens group and a rear lens group, said zoom lens being provided with said lens drive mechanism according to claim 1, wherein said rear lens group is said lens group supported by said second member.
 19. A zoom lens including front and rear lens groups, said zoom lens being provided with a rear lens group drive mechanism for driving said rear lens group to move along an optical axis direction relative to said front lens group, said zoom lens comprising:a shutter mounting stage which supports a shutter comprising a plurality of shutter blades; a lens supporting member which supports said rear lens group, said lens supporting member being movable along said optical axis relative to said shutter mounting stage without rotating about said optical axis; a guide shaft extending in a direction of said optical axis, said guide shaft being supported on said shutter mounting stage to be guided in said direction of said optical axis, a rear end of said guide shaft being secured to said lens supporting member; a gear rotatably supported on said shutter mounting stage, said gear being mounted to be immovable in said direction of said optical axis relative to said shutter mounting stage, said gear defining a hole at an axial center, and a first thread formed on an inner periphery of said hole; a screw shaft on which a second thread is formed said screw shaft extending parallel to said guide shaft, a rear end of said screw shaft being secured to said lens supporting member, said gear being rotatably fitted to said screw shaft with said first thread meshing with said second thread; a drive mechanism for driving said gear to rotate about said screw shaft; a stopper plate secured to another end of each of said screw shaft and said guide shaft; and an impact absorbing member fitted on said guide shaft adjacent to said stopper plate.
 20. The zoom lens according to claim 19, wherein said impact absorbing member is slidable along said first guide shaft.
 21. The zoom lens according to claim 19, further comprising a first moving barrel, a second moving barrel and a third moving barrel concentrically arranged in this order from said optical axis, wherein said first moving barrel supports said shutter mounting stage therein.
 22. The zoom tens according to claim 19, wherein said impact absorbing member is an O-ring. 